HR: 0800h
AN: PP11B-0563    [Abstracts]
TI: Sedimentology, Petrology, and Volcanology of the Lower Aptian Selli Event (OAE1a) on the Shatsky Rise, North-Central Pacific Ocean
AU: * Marsaglia, K M
EM: kathie.marsaglia@csun.edu
AF: Department of Geological Sciences, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330-8266 United States
AB: The large-scale submarine volcanism documented across the Pacific at ~120 Ma also affected the Shatsky Rise. The interval containing the lower Aptian Selli Event (OAE1a) was cored on the Shatsky Rise during Ocean Drilling Program Leg 198 with moderate (50%) recovery. Thin sections were produced from the Selli organic-rich interval, as well as the tuffaceous units above and below it. Mineralogy of selected samples was determined using X-ray diffraction analyses. On the Shatsky Rise, there is a pulse of ash input just prior to the deposition of the Selli OAE1a interval. Its texture and alteration are consistent with a mafic source, either a direct product of Ontong Java Plateau eruptions or more likely, an indirect product via reactivation of the older volcanic edifices on the rise. Soon after this volcanic pulse, anomalous amounts of organic matter accumulated on the rise forming a black shale horizon. The complex textures in the organic-rich intervals suggest a history of periodic anoxia, overprinted by bioturbation. Components include pellets, radiolaria, and fish debris. Petrographic observations made across the well-developed OAE1a interval at Site 1207 indicate that at the beginning of the event, the organic matter had a more globular texture (sapropellic algal matter) that progressively became laminated upsection. What this likely represents is the onset of organic matter accumulation and the resultant development of bacteria colonies on the sediment surface. These laminae are first irregular and discontinuous (wispy), then become more continuous and dense. The presence of carbonate-cemented radiolarite under the Selli interval implies carbonate remobilization, perhaps linked to calcareous microfossil dissolution. The volcanic debris in the overlying tuffaceous interval differs in that it is mainly epiclastic and glauconitic, likely derived from an emergent volcanic edifice on the Shatsky Rise. The epiclastic debris is mostly microlitic and locally tachylitic, suggesting that source lavas cooled slowly as would be expected in a subaerial setting. Rounding of the epiclastic debris is consistent with transport in a beach setting or possibly a high-energy shelf. The time frame involved with this interval (tuffaceous and organic-rich units) is relatively short, on the order of 1 million years, which would be consistent with the timeframe need for the rejuvenation and then subsidence of volcanic centers. This story, although best told through the stratigraphic section on the Shatsky Rise, is also represented in the Mid-Pacific Mountains at Site 463.
DE: 8404 Ash deposits
DE: 9355 Pacific Ocean
DE: 9609 Mesozoic
DE: 3675 Sedimentary petrology
DE: 3022 Marine sediments--processes and transport
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting